Committee on Evolutionary Biology, University of Chicago, Chicago, IL, USA.
Mol Biol Evol. 2010 Apr;27(4):848-61. doi: 10.1093/molbev/msp291. Epub 2009 Dec 14.
A central goal of evolutionary genetics is an understanding of the forces responsible for the observed variation, both within and between species. Theoretical and empirical work have demonstrated that genetic recombination contributes to this variation by breaking down linkage between nucleotide sites, thus allowing them to behave independently and for selective forces to act efficiently on them. The Drosophila fourth chromosome, which is believed to experience no-or very low-rates of recombination has been an important model for investigating these effects. Despite previous efforts, central questions regarding the extent of recombination and the predominant modes of selection acting on it remain open. In order to more comprehensively test hypotheses regarding recombination and its potential influence on selection along the fourth chromosome, we have resequenced regions from most of its genes from Drosophila melanogaster, D. simulans, and D. yakuba. These data, along with available outgroup sequence, demonstrate that recombination is low but significantly greater than zero for the three species. Despite there being recombination, there is strong evidence that its frequency is low enough to have rendered selection relatively inefficient. The signatures of relaxed constraint can be detected at both the level of polymorphism and divergence.
进化遗传学的一个核心目标是理解导致观察到的变异的力量，包括物种内和物种间的变异。理论和实证研究表明，遗传重组通过打破核苷酸位点之间的连锁，有助于这种变异，从而使它们能够独立地表现，并使选择因素能够有效地对它们起作用。果蝇的第四号染色体被认为没有或很少发生重组，它一直是研究这些效应的重要模型。尽管之前已经做了很多努力，但关于重组的程度以及对其起作用的主要选择模式的核心问题仍然没有答案。为了更全面地检验关于重组及其对第四号染色体上选择的潜在影响的假设，我们对来自果蝇、模拟果蝇和雅库巴果蝇的第四号染色体上的大多数基因进行了重新测序。这些数据与现有的外群序列一起表明，对于这三个物种，重组虽然很低，但明显大于零。尽管存在重组，但有强有力的证据表明，其频率足够低，使得选择相对低效。在多态性和分歧的水平上都可以检测到放松约束的特征。
